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.TH PTHREAD_BARRIER_WAIT 3C "Jan 30, 2004"
.SH NAME
pthread_barrier_wait \- synchronize at a barrier
.SH SYNOPSIS
.LP
.nf
cc \fB-mt\fR [ \fIflag\fR... ] \fIfile\fR... [ \fIlibrary\fR... ]
#include <pthread.h>

\fBint\fR \fBpthread_barrier_wait\fR(\fBpthread_barrier_t *\fR\fIbarrier\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBpthread_barrier_wait()\fR function synchronizes participating threads at
the barrier referenced by \fIbarrier\fR. The calling thread blocks until the
required number of threads have called \fBpthread_barrier_wait()\fR specifying
the barrier.
.sp
.LP
When the required number of threads have called \fBpthread_barrier_wait()\fR
specifying the barrier, the constant \fBPTHREAD_BARRIER_SERIAL_THREAD\fR is
returned to one unspecified thread and 0 is returned to each of the remaining
threads. At this point, the barrier is reset to the state it had as a result of
the most recent \fBpthread_barrier_init\fR(3C) function that referenced it.
.sp
.LP
The constant \fBPTHREAD_BARRIER_SERIAL_THREAD\fR is defined in
<\fBpthread.h\fR> and its value is distinct from any other value returned by
\fBpthread_barrier_wait()\fR.
.sp
.LP
The results are undefined if this function is called with an uninitialized
barrier.
.sp
.LP
If a signal is delivered to a thread blocked on a barrier, upon return from the
signal handler the thread resumes waiting at the barrier if the barrier wait
has not completed (that is, if the required number of threads have not arrived
at the barrier during the execution of the signal handler); otherwise, the
thread continues as normal from the completed barrier wait. Until the thread in
the signal handler returns from it, it is unspecified whether other threads may
proceed past the barrier once they have all reached it.
.sp
.LP
A thread that has blocked on a barrier does not prevent any unblocked thread
that is eligible to use the same processing resources from eventually making
forward progress in its execution.
.sp
.LP
Eligibility for processing resources is determined by the scheduling policy.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, the \fBpthread_barrier_wait()\fR function returns
\fBPTHREAD_BARRIER_SERIAL_THREAD\fR for a single (arbitrary) thread
synchronized at the barrier and 0 for each of the other threads. Otherwise, an
error number is returned to indicate the error.
.SH ERRORS
.sp
.LP
The \fBpthread_barrier_wait()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The value specified by \fIbarrier\fR does not refer to an initialized barrier
object.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.sp
.LP
.BR pthread_barrier_destroy (3C),
.BR attributes (7),
.BR standards (7)
